The present invention generally relates to absorbent fibrous paper-based structures such as hand towels, tissues, wipers, and the like, and more specifically, to compressed absorbent fibrous structures.
Absorbent fibrous structures, such as hand towels, wipers, tissues, and the like, as well as various components for other fluid-handling and absorbing materials are well known in the art. These structures may be formed from materials that allow them to be absorbent so that the structures will typically absorb, in varying degrees, liquids from one""s body or elsewhere. Such liquids may include water, coffee, milk, cleaning formulations, oil, etc., and various bodily fluids such as blood, urine, nasal discharge and other body exudates. Various natural wood pulp fibers, as well as synthetic fibers, may be useful for making such fibrous structures.
Often, absorbent fibrous structures such as hand towels (commonly referred to as xe2x80x9cpaper towelsxe2x80x9d) will be wound onto various types of paperboard cores. These paperboard cores, with towels wound onto them, may be placed in various types of dispensing mechanisms to allow users to dispense one or more towel at a time from the roll. The rolls of towels may be perforated at various points to divide bulk rolls into single sheet towels. During dispensing, a user may tear one or more towels along the perforation lines for use. When the towels are not perforated, teeth may be provided on the dispenser for assisting in tearing the roll into individual towels.
Due to the bulkiness of the paper rolls, only a defined number or length of towels, and thus a defined number of drying uses, may be available from each roll. This number of drying uses may be typically referred to as the number of hand dries available.
The size of the paper rolls, and thus the resulting number of hand dries, may be limited by the size of the dispensers in which the rolls may be kept. Most standard-sized roll towel dispensers may accept a paper towel roll of approximately 8 to 9 inches in diameter. Often, use of the paper towels from the roll must be monitored and the dispenser must be refilled frequently in order to prevent depletion of the product.
Some paper towels, on the other hand, may be provided in a folded condition with multiple towels stacked on top of one another. In such arrangements, a single towel may be dispensed one at a time. Often, like the roll towel dispensers, the dispensers in which folded towels are stacked and dispensed also may have a limited capacity and must, likewise, be monitored and refilled frequently.
Towel run-out occurs when the towels within a dispenser are exhausted and a janitor has not yet replenished the dispenser with a fresh or additional supply of new towels. Towel run-out may be one of the most common complaints from hand towel end users. Preventing towel run-out may require either more frequent visits by the janitor or the addition of more towels in the dispenser. The former solution is most likely not desired by towel end users or the entities that purchase the towels for end use because an increase in janitorial visits obviously increases labor costs. It seems that the latter solution has not heretofore been workable because of the fixed sizes of the dispensers and the thicknesses of the typical towels.
Even when rolls of towels are added on a frequent basis, the presently-employed roll towels may result in significant waste. Often, it will be necessary to replace a roll of towels prior to completely using the entire roll in order to prevent towel run-out. The amount of towels remaining on the roll may not justify continued utilization of the remainder of towels on the roll and, thus, the remainder of the yet-to-be-used towels are often discarded along with the core.
It has generally been perceived that the bulkier, or thicker, that a paper towel, tissue, or wiper is, then the more absorbent and xe2x80x9csofterxe2x80x9d it is. While such attributes are desirable and may be obtained by creating fibrous structures with greater thicknesses, the additional thickness creates numerous disadvantages. For example, as the thickness of a towel increases, the number or length of towels, and thus the number of drying uses, that can be placed inside a standard dispenser decreases.
Another consideration that is a disadvantage when using conventional-sized towels is that there is a defined number of hand dries per case of towel rolls or case of folded towel packages. It would be desirable from a shipping cost standpoint (both freight and shipping materials cost) and from a storage standpoint to fit more hand dries into each case of towels. In particular, the end user would need to store fewer cases of towels at its facilities if more hand dries could be found in a case.
Moreover, when using rolled towels, the inner core upon which the towels are wound must be disposed of. The more towels that can be placed on a roll, the less frequent is the disposal of such cores. If additional numbers of towels could be wound onto a roll, conservation and recycling efforts could be enhanced by allowing a core to be used for a longer period of time.
The present invention addresses some of the needs outlined above and provides an improvement to towel run-out and excessive waste by providing more towels within a standard-sized towel dispenser.
U.S. Pat. No. 5,779,860 to Hollenberg et al., which is commonly owned by the assignee of the present invention is directed to a product and process that utilizes compression techniques to increase the density of and decrease the caliper of various webs so that space-saving towels of the type discussed herein may be obtained. However, the absorbent structures discussed therein are compressed into structures that will have a thickness of less than about 50% of the thickness of the original uncompressed structure. In other words, the uncompressed webs of Hollenberg et al. are compressed so as to increase their densities at least about 50%. For example, an uncompressed web having a density of about 0.2 grams per cubic centimeter may be compressed so that its density is increased to about 0.3 grams per cubic centimeter or greater. In particular, the webs containing high yield pulps, such as bleached chemithermomechanical pulp, may be compressed at such ranges and still maintain their structure and wet strength. In fact, when saturated with water, the density of such compressed webs will decrease about 20 percent or greater. As discussed herein the present inventive webs provide certain of the advantages of the webs described in Hollenberg et al., but are formed from different materials and with different processes.
In accordance with the present invention, certain advantages are accomplished by compressing a paper web that has a temporary or permanent wet strength. The resulting paper web may allow more feet of towels to be added to a towel roll (or more towels to be added to a stack of folded towels) without substantially increasing the diameter of the roll (or the thickness of the stack of towels). More sheets on a roll (or more towels in a folded towel stack) may mean fewer roll (or folded towel) changes and replenishings for the end user. Fewer rolls per case and a reduced case size may translate into fewer cores and shipping cases to be disposed of. The invention may also allow more towels to be shipped on the same truck or placed into a standard shipping storage compartment.
A compression force may be applied to the paper web to provide a compressed paper web having a certain reduced caliper. The amount of compression applied to the paper web may be expressed as a xe2x80x9ccaliper compression ratioxe2x80x9d as defined herein.
Desirably, the caliper compression ratio will be between about 0.1 and about 0.5 in order to meet the requirements of the present invention.
In addition, the compressed webs of the present invention will have a water absorbent capacity of at least about 70% of the water absorbent capacity of the same web prior to compression, desirably at least about 80%, and even more desirably at least about 90%.
The presently inventive compressed webs have also been found to xe2x80x9cspring backxe2x80x9d, or expand, to a certain extent upon wetting. Such expansion may allow the webs to recover as much as from about 60% to about 150% of their original dry uncompressed caliper when wet after being compressed.
The sponge-like action of these compressed webs allows them to maintain absorbency characteristics similar to those of the original, uncompressed web. However, because the webs are compressed, more towels may be placed inside a single dispenser, whether the dispenser is for holding folded towels or for holding towels on a roll core. In any event, the frequency of monitoring the towel supply may be reduced by employing the presently compressed webs. In addition, the frequency of excessive waste discards may also be reduced by employing the present invention.
The compression required by the present invention can be imparted by several different processes. For example, an extra calendering step may be utilized or, in one alternative, increased pressure may be imparted to the original calendering rolls utilized in a process for making the fibrous absorbent structure.
Various fibers may be employed in forming the webs of the present invention. For example, wood pulp fibers, in 100% amounts, may be utilized. Alternatively, mixtures of wood pulp fibers with other types of fibers, including various synthetic fibers such as meltblown and spunbonded fibers may be used. In addition, other types of fibers and filaments may be used to provide a desired resiliency to the webs. For example, fibers produced from chemical thermal mechanical pulping processes and thermal mechanical pulping processes, or other high yield pulping processes, as well as curled fibers that are produced by various methods such as by high-consistency refining, and fibers that are internally cross-linked may be employed.
While various types of webs may be utilized in forming the compressed absorbent fibrous structures of the present invention, webs produced according to the uncreped through-air dried, heavy wet creped, and light dry creped processes described herein provide favorable compressed towel products that exhibit acceptable consumer-desired characteristics such as absorbency and feel.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.
Reference now will be made in detail to the embodiments of the invention, one or more examples of which are set forth below.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present invention are disclosed in or are obvious from the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.
In general, the present invention relates to compressed webs useful in forming absorbent fibrous structures such as paper towels and the like. In addition, the present compressed webs could be used for other absorbent applications such as components of diapers, bed pads, feminine hygiene products, incontinence products, and the like. When the present compressed webs are utilized in the above-mentioned and other absorbent products, thinner, less bulky products are available to the consumer. Such thinner, less bulky absorbent products allow for certain advantages in storage space, in dispensing space, and, when the absorbent product is worn by a consumer, in comfort for the wearer.
Despite being compressed, and contrary to conventional wisdom, the towels and other absorbent structures formed according to the present invention do not substantially lose the necessary absorbent capacity to function as absorbent structures. In addition, the absorbent structures maintain desirable characteristics such as feel and other qualitative aspects.
The webs may be made from various fibers, including various cellulosic fibers such as natural wood pulps in conjunction with various additive fibers, including fibers made from synthetic resins. The fibers useful for making the sheets of the present invention may be wet resilient fibers that include various high yield pulp fibers, flax, milkweed, abaca, hemp, cotton or any of the like that are naturally wet resilient or any wood pulp fibers that are chemically or physically modified. Such pulp fibers may include fibers that are crosslinked or curled so that they have the capacity to recover after deformation in the wet state, as opposed to non-resilient fibers that may remain deformed and do not recover after deformation in the wet state.
Desirably, the absorbent structure must be sufficiently dimensionally stable so that the web will avoid collapsing when the web is contacted with water. Without such resiliency, the compressed web would be relatively useless for the various absorbent end uses contemplated by the present invention.
As known in the art, various materials may be utilized to add additional wet strength to the resulting compressed absorbent structures. Such wet strength agents are commercially available from a wide variety of sources and some of such agents are generally described in U.S. Pat. No. 5,779,860 to Hollenberg et al., which is incorporated herein in its entirety by reference thereto. Any material that, when added to a paper or tissue, results in providing a wet strength to dry strength ratio in excess of 0.1 will be considered a suitable wet strength agent. Such agents are generally classified as xe2x80x9cpermanentxe2x80x9d or xe2x80x9ctemporaryxe2x80x9d wet strength agents. Permanent agents provide a product that retains more than 50% of its original wet strength after exposure to water for a period of at least five minutes; temporary agents provide a product that retains less than 50% of its original wet strength after exposure to water for five minutes. Such agents, whether permanent or temporary, are typically added to pulp fibers in an amount of at least about 0.1 dry weight percent, and usually in an amount of from about 0.1 to about 3 dry weight percent, based on the dry weight of the pulp fibers.
Desirably, the absorbent webs of the present invention will be made according to the uncreped through air-dried, heavy wet creped or light dry creped. The webs of the present invention, after being formed, are then compressed by exerting on them a certain force per linear inch while passing through one or more calendering or supercalendering roll arrangements. Mechanisms other than calendering processes may also be employed to supply the necessary compressive forces.
As used herein, the term xe2x80x9ccalenderxe2x80x9d refers to a process for fabrics or nonwoven webs that reduces the caliper and imparts surface effects, such as increased gloss and smoothness. Generally, the process includes passing the fabric through two or more heavy rollers, sometimes heated, and under high nip pressures.
Processes for forming uncreped through-air dried webs are described in U.S. Pat. No. 5,779,860 to Hollenberg et al. and U.S. Pat. No. 5,048,589 to Cook et al., both of which are assigned to the assignee of the present invention and both of which are incorporated herein in their entireties by reference thereto. In such processes, through air drying is employed as shown in the Figures of Cook et al. As described and shown therein, a web is prepared by: (1) forming a furnish of cellulosic fibers, water, and a chemical debonder; (2) depositing the furnish on a traveling foraminous belt, thereby forming a fibrous web on top of the traveling foraminous belt; (3) subjecting the fibrous web to noncompressive drying to remove the water from the fibrous web; and (4) removing the dried fibrous web from the traveling foraminous belt. The process described therein does not include creping and is, thus, referred to as an uncreped through-air drying process.
Towels prepared from this uncreped through-air drying process will typically possess relatively high levels of absorbent capacity, absorbent rate, and strength. In addition, because the process avoids the use of costly creping steps, towels produced according to such a process will generally be more economical to produce than creped towels of similar composition and basis weight.
A process that produces a noncompressed sheet using can drying which may be employed in the present invention is described in U.S. Pat. No. 5,336,373 to Scattolino et al., which is incorporated herein in its entirety by reference thereto.
The caliper of the webs prior to compression according to the present process will typically be in the range of from about 0.005 (0.127 mm) to about 0.030 (0.762 mm) inches. After compression, a compressed web of the present invention will typically have a caliper of from about 50% to about 90% of its original caliper.
As used herein xe2x80x9ccaliperxe2x80x9d refers to the thickness of a sheet or web. Caliper has been measured in the following examples utilizing an EMVECO Model 200-A with the following specifications: pressure foot lowering speed of 0.8 millimeter/second; surfaces of pressure foot and anvil parallel to within 0.001 millimeter; capability of repeated readings within 0.001 millimeter at zero setting or on the calibrated gage; a flat ground circular fixed face (anvil) of a size that is in contact with the whole area of the pressure foot in the zero position; capacity of 0-12.7 millimeter; sensitivity of 0.025 millimeter; load of 2.0 kiloPascals; anvil area of 2500 square millimeters; and an anvil diameter of 56.4 millimeters.
The compressed webs may be characterized as having a certain caliper compression ratio. The xe2x80x9ccaliper compression ratioxe2x80x9d as used herein is defined by the following equation:       (                  caliper        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        uncompressed        ⁢                  xe2x80x83                ⁢        web            -              caliper        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        compressed        ⁢                  xe2x80x83                ⁢        web              )        caliper    ⁢          xe2x80x83        ⁢    of    ⁢          xe2x80x83        ⁢    uncompressed    ⁢          xe2x80x83        ⁢    web  
In the present webs, the caliper compression ratio would be between about 0.1 and about 0.5.
In addition, the compressed web may have an absorbent capacity sufficient to allow it to absorb liquids and function similarly to the same web in an uncompressed state. The absorbent capacity refers to the amount of liquid that can be absorbed by the paper web. Absorbent capacities discussed herein are defined according to the grams of water (or oil) absorbed by the absorbent structure divided by the weight in grams of the structure absorbing the water (or oil). The absorbent capacity of a sheet for oil indicates the internal void volume of the sheet. As the sheet is compressed, the internal void volume decreases.
The absorption capacity of paper products (either their water or oil absorbent capacities) may be determined according to the following procedure. A pan large enough to hold water to a depth of at least 2 inches (5.08 cm) is filled with distilled water (or oil). A balance, such as the OHAUS GT480 balance described herein, is utilized in addition to a stopwatch. A cutting device, such as that sold under the trade designation TMI DGD by Testing Machines, Inc., of Amityville, N.Y., and a die with dimensions of 4 inches by 4 inches (xc2x10.01 inches) (10.16 cm by 10.16 cmxc2x10.25 cm) are also utilized. Specimens of the die size are cut and weighed dry to the nearest 0.01 gram. The stopwatch is started when the specimen is placed in the pan of water (or oil) and soaked for 3 minutes xc2x15 seconds. At the end of the specified time, the specimen is removed by forceps and attached to a hanging clamp to hang in a xe2x80x9cdiamondxe2x80x9d shaped position to ensure the proper flow of fluid from the specimen. In addition, the specimen is hung in a chamber having 100 percent relative humidity for 3 minutes xc2x15 seconds. The specimen is then allowed to fall into the weighing dish upon releasing the clamp. The weight is then recorded to the nearest 0.01 gram.
The absorbent or absorptive capacity of each specimen is then calculated as follows:
Absorbent Capacity (g)=Wet weight (g)xe2x88x92Dry weight (g)
Obviously, the particular absorbent capacity of a web depends on a variety of factors including its basis weight and its composition. Thus, webs having a variety of absorbent capacities may be utilized in the present invention and often depend largely on the needed capacity for the intended end use of the absorbent structures.
The present compressed webs will typically have a water absorptive capacity which is at least about 70% of the water absorptive capacity of an uncompressed paper web formed from the same materials by the same process and having an identical basis weight.
As used herein, xe2x80x9cbasis weightxe2x80x9d refers to the mass per unit area of a web and is reported as grams per square meters or xe2x80x9cgsmxe2x80x9d. Basis weight is measured by cutting a sample portion of a web and then subjecting that sample portion to the following procedure. A balance with a capacity and sensitivity to weigh to about 0.001 gram for specimens weighing under about 10 grams and to about 0.01 grams for specimens weighing about 10 grams and more is utilized. An exemplary balance that may be employed is sold under the trade designation OHAUS GT210 by VWR Scientific Product of South Plainfield, N.J. The standard weights for a balance range from about 10 milligram to about 100 grams. If a level is not supplied with the balance, then a sealed glass vial may be utilized. The weighing pan should be of a size large enough to hold the specimen without it hanging over the pan. Desirably, the minimum die size for a single specimen will be 4.5xc2x10.1 inches (114xc2x13 mm) by 4.5xc2x10.1 inches (114xc2x13 mm). If multiple smaller specimens are utilized, then any known size die would be appropriate. The ruler will be graduated in 0.1 inches or 1 mm increments.
Test specimens obtained from the webs would be free of folds, wrinkles, or any distortions. Desirably, all specimens would have a minimum area of at least 20 square inches (130 square centimeters) or a number of smaller die-cut specimens would be taken from different locations in the sample with a minimum total area of at least square inches (130 square centimeters). Each specimen would then be weighed and recorded.
Basis weights are then calculated by determining the area of the sample(s) in square inches. Then, the weight of the specimen(s) measured in grams is divided by the area. This value is then multiplied by a factor to obtain the desired units. The conversion factors for multiplying by (weight/area) are as follows:
Prior to testing any of the presently inventive webs, the sheets were conditioned at ASTM conditions of 50% relative humidity xc2x12% and at 72xc2x0 F.xc2x12xc2x0 (22.2xc2x0 C.xc2x11.1xc2x0) for at least 24 hours.
Another characteristic of the present inventive webs is their ability to recover a major proportion of their original thickness, or bulkiness, that existed prior to compression. In other words, the webs are capable of expanding upon being exposed to water and will return to at least about 60% of their original uncompressed wet caliper, and desirably to at least about 80% of their original uncompressed wet caliper. Wet caliper refers to the caliper of a particular web after it is immersed in water for 30 seconds and then allowed to hang for one minute to allow the excess water to be removed therefrom.
In one particular example, a 22 lbs/ream of 2880 square feet basis weight paper web made according to the uncreped through-air drying process described above and made from a pulp furnish of 70% recycled fiber and 30% Mobile pine pulp obtained from the Kimberly-Clark pulp mill in Mobile, Ala., may be utilized. When the compressed web (having its caliper reduced 22% by compression) having this formulation was tested in a wet state against the same web in an uncompressed wet state, evaluators of the web""s characteristics did not perceive a statistically significant difference in the overall quality, drying effectiveness, absorption rate or substantial feel between compressed and uncompressed towels.
In one study, towels in various compressive states were analyzed. For example, a roll that would normally be 800 feet in length in an uncompressed state was compressed so that the same diameter roll would result in a roll having 1000 feet in length (a 25% increase) and in a roll having 1200 feet in length (a 50% increase). The average length of uncompressed paper towels used per hand dry was 23.5xe2x80x3 while the average length of compressed paper towels (at a compression of 25%) was 24.7xe2x80x3 and the average length of compressed paper towels (at a compression of 50%) was 24.3xe2x80x3.
Various processes may be employed to compress the presently inventive webs and the present invention is not limited to the use of any particular compression process. As is known in the art, passing sheets through one or more rollers or nips will compress and smoothen the surfaces of the sheet materials. The equipment employed to apply the compressive force are generally referred to as calenders or supercalenders. Obviously, the effect of calendering on a particular structure depends on the temperature, the pressure applied, and the duration of the pressure, with all three factors being variable to obtain the desired calendering results.
In compressing the webs of the present invention, an extra calendering step may be utilized or, in one alternative, increased pressure may be imparted to the original calendering rolls utilized in a process for making the fibrous absorbent structure. Various calendering techniques such as hot or steam calendering may be alternatively employed to produce the compressed absorbent webs.
Alternatively, the webs can be compressed using flat platten presses or fabric nips used to smooth and compact multiwiper products as disclosed in U.S. Pat. No. 5,399,412 to Sudall et al., which is incorporated herein in its entirety by reference thereto. In this manner, the resulting sheets of the present invention could have areas that are highly compressed and areas that are less compressed or not compressed at all.
Such compressing processes are generally described as imparting a certain force per linear inch on the paper web and are reported in pounds per linear inch (xe2x80x9cPLIxe2x80x9d). The xe2x80x9cnip pressurexe2x80x9d is another term used herein and refers to the pressure at the calendering nip. Nip pressure is defined by dividing the force per linear inch by the width of the nip formed between the calendering rollers.
The following examples are meant to be exemplary procedures only which aid in the understanding of the present invention. The invention is not meant to be limited thereto.